1. Field of the Invention
The present invention relates generally to plating baths and methods for monitoring the constituents contained therein. More particularly, the present invention relates to a method for preconditioning an electrode used to monitor plating bath constituents.
2. Description of Related Art
A typical plating bath solution is comprised of a combination of several different electrochemical constituents. The specific constituents vary depending upon the type of plating bath, but in general can be broadly divided into what are commonly known as major constituents and minor, or trace, constituents. It has long been recognized that appropriate levels of both major and trace constituents must be maintained to consistently produce high quality, reliable plated material at low cost. The monitoring and control of plating baths is therefore a major concern to the electronics, automotive and general electroplating industries.
Voltammetric signal analysis provides an efficient means for monitoring a plating bath solution. One such monitoring process is described in U.S. Pat. No. 4,631,116, assigned to the present assignee. The method disclosed therein applies a combined ac and dc voltammetric signal to an electrode in contact with the plating solution to produce ac current spectra which indicate trace constituent concentration levels. In order to achieve accurate, repeatable and robust results, plating bath analysis methods such as these include a means for preconditioning the electrode to yield a reproducibly clean and reactive electrode surface. In U.S. Pat. No. 4,631,116, the electrode is pretreated by applying one or more anodic voltages for a certain period of time prior to the measurement of the ac spectra. The voltage and application time of the pretreatment signal are varied to determine the settings which provide the best measurement repeatability for a particular constituent.
For certain types of plating baths and constituents, however, anodic preconditioning alone may not produce adequate measurement accuracy and repeatability. In a chromium plating bath solution, for example, repeatable and robust results are difficult to obtain regardless of the voltage and duration of the anodic preconditioning signal. Similar problems may arise with other types of plating baths. In such a situation, the benefits of the monitoring process are lost as a result of inadequate electrode preconditioning.
As is apparent from the above, there presently is a need for a simple and versatile preconditioning method which improves monitoring accuracy and repeatability for a wide variety of plating baths and constituents. The method should provide an alternative preconditioning technique suitable for use in those situations where anodic preconditioning alone yields unsatisfactory results. Furthermore, the method should be compatible with existing voltammetric analysis systems, thereby expanding the measurement capability of those systems without requiring additional equipment.